Correct ( Good ) Ignition time

[novaes]

1) Please, what is the correct ( Good ) ignition time for BSA A10 Golden Flash Plunger 1951 Engine number ZA10 - 10074 ? I use piston compression ratio 8: 1 .
2) What is the correct valves clearances for Inlet and Exhaust ?

Novaes- Brazil

[shabashow]

Hi Novaes,
according to the BSA service sheet the inlet clearance is 0.010 inches and the exhaust is 0.016 inches.
Ignition timing is measured as distance before Top Dead Centre and should be 11/32" before TDC, just as the points are opening, and the ignition fully advanced.
You have to remove the outer timing cover and wedge the auto advance unit so that it is at maximum advance. The spark plug needs to be removed and a rod put in vertical to get where TDC is. Mark that rod against something on the head that won't move, then mark it again 11/32 higher. Then turn the engine backwards a bit (probably best by putting it in gear and turning the back wheel) Then turn the engine fowards until the 11/32" mark is at the right point against where you measured TDC. The points in the magneto should just be starting to open. You can nmeasure that with a thin cigarette paper. It will just start to get loose as the points open.
good luck - I'll be doing exactly the same tomorrow night, as my 1952 Plunger seems to be running a bot retarded.
John

[LJ.]

Hi Novaes... To add a little more to what John has said...

The crucial part is getting the auto advance component to fit on the magneto taper Without it slipping! It is difficult because it can turn when you proceed to tighten up the nut. Firstly make sure the taper, both on magneto and inside the auto advance, have clean surfaces, free of all dirt grease and oil. Use some cellulose or alcohol to clean, this will give a clean dry surface. When you have carried out the timing proceedures as John has explained, use a sharp tap with a hammer to allow the auto advance component to initially stick on the taper with magneto. You should then be able to tighten up the nut carefully at first with smaller risk of it all slipping. Good Luck! 

[shabashow]

Good advice, LJ. Maybe that's why my timing has become retarded so quickly.
John

[RichardL]

Dave, et al,

I happen to be woriking on timing, right now, also. Last night I made too many failed attempts to get it just right. The problem is, as you say, slippage after getting the gap set to the minimun opening. It makes me wonder if I am trying to be too precise. The triple complication of setting the minimum gap while the points block tries to ride the shelf in the magneto ring, tightening of the pinion without going off that shelf, and maintaining the piston at the correct height before before TDC, together, are daunting. So, I think they did not try as hard as I (or, us) to meet exact values. Nevertheless, I will probabaly proceed with the mutliple attempts until I match the values, because, I don't know how far astray is too far. Incidentally, it has been many, many years since I have needed cigarette papers.

With regard to tapping the auto-advance pinion to seat the taper, that sounds like a good idea and will do it, maybe in an hour or so. However, I think it probabaly needs to be done with a socket over the bolt, otherwise you are just beating on the threads and, I think, not seating the taper.

Richard

[LJ.]

Richard... I can't remember the bolt arrangement of the auto advance mechanism but I do know it is an ingenious little fella that has a double job of tightening the mechanism to the magneto and also undoing and pulling off the taper when removal is required. A beating is not neccessary because I found that the clean dry tapers only need just 'one' sharp tap to intitially hold all together while gently tightening up, keeping a very close eye open for any movement. You can then slowly progress to tighten up harder as the taper is pulled together tighter.

Hope this reaches you before you go back to the workshop. BTW try and be as precise as you can because then you wont be out all that much if you do slightly slip.

Good Luck!

[G/F DAVE]

LJ  is right what ever you do dont tap auto advance mechanism as there is a outer thread on the centre nut that extracts the pinion, so if you hit pinion you are going to damage this thread .If you tighten centre pinion nut until you can just turn the points at other end of mag then set your crankshaft at the right place then turn the points till your fag paper is just freeing itself with auto advance opened then you just nip the centre nut only a little to tighten taper. then turn engine over a couple of times to make sure it 100% on both cylinders, once happy I use a socket on crankshaft to hold steady while I tighten pinion nut. then recheck By the way I use a little device that has a buzzer which sounds once the points break which is a lot easier than fiddling with fag papers, but as they cost aroung £45.00 gbp I borrow mine from my mate who works on tiger moths. Ignition timing is most important on these engines, I have modified a old pinion with timing marks on so I can then spin up the magneto and use a strobe to check difference between the cylinders if there is any can this be evened out with a oil stone.I know it,s a lot of time consuming but I personally think it,s worth it. Good Luck GF/DAVE

[RichardL]

Gents,

Thanks for the comments. I did not get back to the shop, so all were and are timely. I won't get back to it until, at least, Wednesday, so any further comments, advice, warnings or "you-must-be-nuts s" will be appreciated.  I don't know why I addressed that last post specifically to Dave, confused, I guess.

I have a couple more questions about tapping the auto-advance mechanism to seat the taper. Assuming I want to follow this, my thinking is to tighten the bolt until the points barely slip but can still be adjusted. Then, slip a socket over the nut so when I tap on the socket so the force goes onto the horseshoe washer area and not on the bolt. It seems to me that tapping on the bolt itself does not seat the taper, but just puts force on the attachment threads. So, is there any way that applying the force at the horseshoe washer damages either the pinion or the removal threads? Then, am I correct that the removal threads will be out of harm's way when the bolt is almost at the point of seating the taper?

I was giving some thought as to how much precision to throw at this problem. I am using a specified 3/8" BTDC based on having 9:1 pistons. I note that the smallest fraction used to describe various values for BTDC is 1/32", as in 11/32" for A10 Golden Flash. The tolerance implied is, thefore, half of this fraction, or, say, 0.015" Using my digital caliper as a depth gauge, I think I should be able to accept the barely open points if they occur anywhere between 0.360" and 0.390", instead of trying to nail it at 0.375" +/- a couple of thousanths.  THOUGHTS?

Richard